Laser beat wave excitation of surface plasma wave and material ablation

Two coplanar laser beams of frequencies ω₁ and ω₂, impinged on a metal surface at angles of incidence θ and -θ, resonantly excite a surface plasma wave (SPW) at the difference frequency ω=ω₁-ω₂ when ω has a specific value ω=ω_R(θ), where ω_r depends on ω₁,ω₂, θ and plasma frequency of the metal. The lasers exert a ponderomotive force on electrons in the skin layer and drive the SPW. The latter heats the electrons efficiently, causing efficient ablation of the material. The reduction in laser pulse lengths results in reducing the efficiency of SPW excitation and ablation.